Other day I needed to convert excel spreadsheet column name to column index when having 200+ columns is easier to express as ‘FB’ instead of 157

A = 0 
B = 1
AA = 26
AA = 27
FB = 157

This code will work for any number of column names.

	/**
	 * Convert given excel column name to column Index, ex 'A=0', 'AA=26'
	 * @param columnName
	 * @return 0 based index of the column
	 */
	private static short convert2ColumnIndex(String columnName) {
		columnName = columnName.toUpperCase();
		short value = 0;
		for (int i = 0, k = columnName.length() - 1; i < columnName.length(); i++, k--) {
			int alpabetIndex = ((short) columnName.charAt(i)) - 64;
			int delta = 0;
			// last column simply add it
			if (k == 0) {
				delta = alpabetIndex - 1;
			} else { // aggregate
				if (alpabetIndex == 0)
					delta = (26 * k);
				else
					delta = (alpabetIndex * 26 * k);					
			}
			value += delta;
		}
		return value;
	}

Converting from index to column name

This process is trivial we simply keep on taking mod 26 from index till we have nothing left, and converting that value to char.